1. Field of the Invention
The present invention relates to a vehicle brake apparatus and, in particular, is comprised of a fluid cooled, circular brake pad arrangement that allows for the increased dissipation of heat for heavy duty braking applications.
2. Description of the Related Art
A typical automotive disk brake includes a circular rotating member called a rotor that is attached to a wheel hub assembly. The rotor and wheel hub are mounted on an axle shaft or spindle of the vehicle via bearings so as to rotate about the axle shaft or spindle. The rotor typically consists of a large diameter flat plate which forms a disk body. The typical disk brake assembly also includes a caliper that has a bracket defining an opening that fits over the outer edge of the rotor. Brake pads are positioned on the inner walls of the opening in the caliper such that a brake pad is positioned adjacent either side of the rotor. The caliper is typically hydraulically, pneumatically or electrically operated such that the pads are urged towards each other to engage with the rotor to slow the speed of rotation of the rotor.
The frictional forces exerted by each pad against each flat metal surface of the rotor will ultimately bring the rotor with attached wheel to a stop, thereby stopping the vehicle. The frictional effect of the pad surface engaging the rotor metal surface creates heat energy that can be dissipated out of the disk brake assembly through a plurality of metal cooling fins that are typically integral to the rotor. The majority of the heat generated by the braking action is dissipated, if at all, through the rotors with very little dissipation of this heat occurring via the brake pad or the caliper because the coefficient of thermal conductivity of the pad is considerably smaller than that of the metal rotor.
The vehicle""s pads and rotors typically have a finite life expectancy. Repeated, hard brakings in stop and go traffic will not allow the brake system to dissipate all the generated heat which causes premature wear on the pads as well as on the rotors. High temperature heating of the rotors contributes to a scoring and glazing of the rotor and pad surface which can reduce the braking effectiveness of the vehicle. Moreover, this heat can cause the rotor to warp over time.
The premature wear pattern and performance limitation of the conventional disk brake system dictate a need for a braking concept that can accommodate more rigorous braking situations. To address these needs, alternative disk brake configurations have been developed.
For Example U.S. Pat. No. 4,508,299 to Cigognini discloses a braking system that includes a rotating rotor with a braking head assembly that has a plurality of cooling passages provided therein. The braking head assembly frictionally engages with the rotating rotor so as to slow the rotating rotor to thereby brake the vehicle. The existence of cooling passages in the braking head assembly increases the cooling capacity of the Cigognini brake assembly and thereby reduces wear on the rotor.
While the Cigognini reference discloses a brake assembly that has improved cooling capacity, the Cigognini brake assembly is difficult to mount and provides only limited cooling capacity. In particular, the movable brake head in the Cigognini assembly is mounted adjacent the rotor via one or more rods that are apparently attached to the frame of the vehicle and extend toward the rotor so as to retain the brake head in proximity to the rotor. This mounting structure requires the installer to mount the rods to the frame of the vehicle which is not always possible with some vehicle configurations. Moreover, due to the relative length of the rods, the braking assembly is more prone to damage and is expensive to manufacture. Further, due to the relative complex mounting assembly for the brake heads, this mounting arrangement makes it difficult for the brake heads to be positioned about more than a limited amount of the circumference of the rotor which results in less braking capability as there is limited surface area of the brake head in contact with the rotor.
Even more significantly, the Cigognini design does not permit the brake assembly to be used in conjunction with brake assemblies that are mounted adjacent movable spindles. In particular, the movable brake head in the Cigognini design moves as a result of actuation of the fixed length rods. Since these rods are permanently attached to the frame of the vehicle, this system cannot be used with brakes on swiveling spindles as the rods do not accommodate any movement of the brake head relative to the rods. Hence, the Cigognini design could not be used on standard automobile front brake systems as the front brakes are attached to swiveling spindles which allow the vehicle to be steered.
It will be appreciated that the majority of braking power that is applied to automobiles and trucks is applied to the front brakes. Consequently, the front brakes are the brakes that are most likely to suffer from excessive heating. The Cigognini design is thus not well suited for use with automobiles, trucks and the like as it cannot be used to cool front brake assemblies that provide the majority of braking for these types of vehicles.
Further, while Cigognini discloses a cooling chamber in the brake head, the fluid in the brake head can flow unimpeded through the brake head. The cooling fluid may therefore be isolated to limited areas of the brake head due to forces on the vehicle during braking. This can lead to isolated areas of the brake head being cooled at different rates than other areas which can, over time, result in damage to the brake head or the rotor. Moreover, the cooling fluid may have to be circulated through the passageway at a faster rate which thereby decreases the efficiency of the heat transfer to the cooling fluid. This can result in limiting the cooling of the brake assembly causing the problems discussed above.
From the foregoing, it will be appreciated that there is a continuing need for brake systems that can provide better brake performance and improve the longevity of the brake components. To this end, there is a continuing need for brake systems with better cooling capability that are less expensive and easier to mount to existing vehicles. More particularly, there is a need for a system for cooling brake components that can be adapted for use with brake assemblies that are movable with respect to the frame of the vehicle, such as the brake assemblies on the front wheels of road vehicles.
The aforementioned needs are satisfied by the brake assembly of the present invention which, in a first aspect, is comprised of a brake assembly having a mounting bracket that is adapted to be positioned about the axle or spindle of a vehicle wherein the mounting bracket has a plurality of arms that extend radially outward from the axle or spindle of the vehicle, a rotor assembly that is rotatably attached to the axle or spindle of the vehicle, and at least one stator that is attached to the mounting arms of the mounting bracket so as to be slidable in a direction that is parallel to the axis of the vehicle axle or spindle such that the at least one stator can engage with the rotor to thereby slow the angular rotation of the rotor wherein the at least one stator is liquid cooled to remove heat generated by the frictional engagement between the rotor and the at least one stator. The assembly further comprises a caliper that defines a cavity that fits around at least a portion of the outer perimeter of the at least one stator and the rotor such that activation of the caliper will result in lateral movement of the stator along the direction of the axis of the axle such that the at least one stator can engage the rotor.
Hence, in this aspect, the brake assembly allows for the use of liquid cooled stators which are better able to remove ambient heat away from the rotor to improve brake performance. Moreover, since the stators are slidably mounted to the mounting arms of the mounting bracket such that the stators can move slidably along pins or guides in a direction that is parallel to the axis of the axle or spindle, installation of the brake assembly is simplified.
In one particular embodiment, two stators are slidably mounted to pins that are positioned on the mounting arms of the mounting bracket such that the rotor can be interposed between two stators. In one implementation, the rotor comprises two circular friction disks attached to the rotor at the stator interface. A caliper assembly can then be positioned about the outer perimeter of the stators such that the stators can be urged inward so as to contact the rotors. In one embodiment, a plurality of mounting arms extend radially outward from the center of the mounting bracket such that a plurality of sliding posts can be positioned about the outer perimeter of the rotor to thereby permit uniform slidable connection points for each of the stators. In this embodiment, a plurality of calipers can thus be used to urge the stators towards the rotor to thereby halt the rotational motion of the rotor.
As the stators are liquid cooled, the stators can remove a greater amount of heat energy occurring as a result of the stators frictionally engaging with friction material positioned on the rotor. In one aspect, each of the stators has channels formed therein that have flow inhibiting structures positioned so as to extend in a direction generally perpendicular to the flow of the cooling fluid to thereby slow the rate of the cooling fluid to allow for greater transfer of heat to the cooling fluid. In another aspect, the cooling fluid is pumped to a cooling reservoir and the stators are also equipped with cooling fins to thereby increase the cooling of the stators to improve the removal of heat from the brake assembly.
It will be appreciated that the brake assembly is better able to remove heat than non-cooled brake assemblies of the prior art and are easier to mount than existing cooled brake assemblies of the prior art. Moreover, since the assembly is mountable via a bracket to the spindle of the vehicle, the brake assembly can be mounted on swivelable front wheels of vehicles thereby permitting cooling of the front brakes of vehicles which typically account for the majority of braking power applied to the vehicle and are more in need of increased cooling capacity. These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.